Hi,
we're seeing occasional ifOutDiscards (interface TX Drops) on 100G Interfaces, even though there shouldn't be any. Closer investigation showed that there really aren't any, but ifOutDiscards SNMP counters sometimes flare up with values that are gone again on the next query. The values that come up often are the same as in a previous cycle, so it appears as if they are stuck somewhere and occasionally manage to become visible. Like so:
[dc-k1-leaf1 14:18:47]
IF-MIB::ifOutDiscards.33 = Counter32: 0
IF-MIB::ifOutDiscards.34 = Counter32: 0
[dc-k1-leaf1 14:18:58]
IF-MIB::ifOutDiscards.33 = Counter32: 5
IF-MIB::ifOutDiscards.34 = Counter32: 1
[dc-k1-leaf1 14:19:09]
IF-MIB::ifOutDiscards.33 = Counter32: 0
IF-MIB::ifOutDiscards.34 = Counter32: 0
[... staying at 0 for a while ...]
[dc-k1-leaf1 14:22:32]
IF-MIB::ifOutDiscards.33 = Counter32: 5
IF-MIB::ifOutDiscards.34 = Counter32: 1
(this was just polling ifOutDiscards.33 and ifOutDiscards.34 every 10s in a loop using snmpget, targeting 1/1/33 and 1/1/34 on a 8360-32Y4C, where these are the first two of the four 100G interfaces).
Given these are Counter32 which should only ever wrap on overflow or maybe when ifCounterDiscontinuityTime says so, the return to zero appears to be a sign of a problem. This is consistent with CLI output regarding these counters being zero (down to the per-queue counters), and with our expectation that some noise in the 100Mbps should not actually trigger TX Drops on a 100G interface. No need to say the above creates funny peaks in graphs monitoring the interfaces in question. It appears to be limited to TX Drops, other counters don't show these flashes of wrong values coming up.
Interfaces I'm focusing on are L3 (IPv4 transit links between leaves and spines, carrying a /31 IPv4). Issue disappears for a while after "clear int statistics global", but comes back after a while. Same with a full switch reboot.
Is this a known phenomenon on this platform? Anybody else seeing this?
Thanks,
Andre.
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Andre Beck
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